Aker River (Akerselven) is a river which flows through Oslo. It starts at Maridalsvannet in Oslomarka, and follows the urban areas, whereby it finally ends at Oslo fjord. The entire river is about 8.2 kilometers long, and has a difference in elevation between source and mouth of approximately 149 meters. Earlier, the river gave power to numerous industry companies in Oslo. Akerselven is “Oslo’s green lung”; many parks and natural trails are to be found by its path, from Grønland to Maridalsvannet. A walk from along Akerselven from the rural Frysja down through the different parts of Oslo all the way down to the city centre is an amazing experience and a walk through the history of Oslo.